1. Field of the Invention
The invention relates to wireless communication networks, and in particular, wireless sensor networks.
2. Introduction
In many wireless sensor networks (WSNs) with star topology, all the wireless sensor nodes except the coordinator are battery powered. The lifetime of such a network is given by the lifetime of the wireless sensor nodes. There are two possible scenarios: (1) the network “dies” when the last wireless sensor node in the network “dies”, and (2) the network “dies” when the first wireless sensor node in the network dies. Maximizing the average capacity of a network described in the first scenario is a trivial exercise. Employing a “winner takes all” approach, the coordinator allocates all the available time slots to the wireless sensor node that has the best channel capacity.
However, doing the same for a network considered in the second scenario is a complicated joint optimization problem. On one hand, the wireless sensor nodes which have good channel capacity should be allocated as many time slots as possible. However, doing so would disproportionally drain the battery of those nodes.
This problem is expanded when a large number of nodes exist in the network that must be placed in wireless sensor node groups. If the wireless sensor nodes are not grouped properly and/or the transmissions time slots are not allocated properly, the network could “die” when one node in one group dies.
Therefore, it is desirable that all the wireless sensor nodes in the network “die” at the same time. If this goal is not achieved, then energy resources in the network are underutilized (i.e. there are nodes which can still transmit).